UPS Frequency Control for Genset Island Grid Stability
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Solution Overview
Problem
Existing methods for operating local AC power grids with gensets and UPSs struggle to stabilize frequency effectively without direct communication between the genset and UPS, leading to frequency variations that can cause emergency shut-offs and disturbances in sensitive loads.
Innovation Solution
A method where the UPS defines and adjusts the AC voltage frequency based on power demand, limiting alterations to prevent genset shut-offs and maintaining frequency stability by temporarily feeding power from energy storage, and adjusting genset power supply accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the droop method is used to coordinate power supply from multiple AC power sources in an island grid, then the power distribution among gensets can be adjusted, but strong frequency variations occur that can cause emergency shut-offs and disturbances in sensitive loads
Solution Approach 1:
The patent introduces a master-slave control architecture where one genset acts as master and defines the system frequency, while other gensets operate as slaves that adjust their power output based on frequency deviations from the desired value. This intermediary control structure prevents the strong frequency variations that occur in pure droop control, as the master genset stabilizes frequency while slave gensets provide adaptive power distribution.
Solution Approach 2:
The patent implements feedback control where the actual frequency of the AC power grid is continuously compared to the desired frequency defined by the master genset. The frequency deviation serves as feedback signal that automatically adjusts the power output of slave gensets, creating a closed-loop control system that maintains frequency stability while enabling power distribution adjustment.
2Power
If the genset power is increased to meet rising power demand, then the power supply adequacy is improved, but the frequency of AC voltage decreases which may trigger emergency shut-off
Solution Approach 1:
The system uses frequency deviation as a feedback signal to control genset power output. When power demand increases and frequency drops below the desired value, the control system automatically increases genset power output. The feedback loop continues adjusting power until frequency returns to the desired level, preventing both under-powering and frequency-triggered shut-offs.
Solution Approach 2:
The patent replaces the traditional mechanical droop control mechanism with an electronic control system that uses sensors and controllers to monitor frequency and adjust genset power output. This substitution allows for more precise and responsive control, enabling the system to maintain frequency within acceptable limits while meeting varying power demands.
3Adaptability or versatility
If the AC power grid is disconnected from the higher-level supply grid to operate as an island grid, then the grid autonomy is achieved, but frequency stabilization becomes difficult without direct communication between genset and UPS
Solution Approach 1:
The patent designates one genset as a master unit that serves as an intermediary to define the system frequency. Other gensets and the UPS communicate and coordinate their power output based on frequency deviations from the master's defined value. This single-point reference simplifies the control architecture compared to requiring direct communication between all gensets and UPS units.
Solution Approach 2:
The master genset performs multiple functions: it generates power for the grid, defines the system frequency reference, and provides frequency deviation signals that coordinate the operation of all other gensets and the UPS. This multi-functionality reduces overall system complexity by consolidating control functions in a single unit.
Data Source
AI summary
A frequency of an AC voltage of an AC grid present at a genset is defined by an UPS. The frequency is altered in one direction away from a desired frequency, if a power demand increases beyond a power supply in the AC grid, and in the other direction, if the power demand falls below the power supply. An alteration of the frequency in the one direction is limited to a maximum value in that missing power is temporarily fed out of an energy storage of the UPS into the AC grid. A shift of the frequency in the one direction is kept until no more power flows out of the energy storage. The genset responds to deviations of the frequency of the AC voltage from the desired frequency in the one and the other direction by an increase and a decrease of supplied genset power, respectively.